480v high leg motor issue

journeyman0217 said:
So is there such thing as a 480v delta high leg? If so, what would be your voltages?
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It is certainly possible to have 480V delta high leg.

You would need a transformer that provides a 480V delta, and one of the 480V coils would have a mid point tap. The midpoint tap would get grounded. If you set this transformer up this way, you would have 480V L-L for all 3 phases, and L-G voltages of 240V, 240V, and 416V.

There is a good diagram midway down this page: https://ctlsys.com/support/four_wire_delta_circuits/
 
journeyman0217 said:
Nobody could ever tell me what they were, thank you
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You are most welcome.

Here is a very typical nameplate from a common Delta -> Wye step down transformer, you can see the 2 dashed lines on the primary and secondary showing a 30 degree phase shift between them. The dotted line on the Delta Primary is "angled" up 30 degrees and the dotted line of the Wye Secondary (at X0) is straight across with zero "angle"

1755097031563.png

Your Delta to Delta coil setups are straightforward and as the current rises in any one primary coil, it does so at the same time in its secondary mate. So zero phase shift and the dotted lines in your nameplate at H1 and X1 show the same angle - with no shift between them.

This phase shift is mostly a nerdy thing and it is very common for them to get misinterpreted as some kind of grounding indications. But they are not, it's science yo ! ;)

Also, sorry this thread is sliding off the rails into the transformer weeds - I assume your motor problem is not related to your transformer.

Again - good luck!
 
MD Automation said:
You are most welcome.

Here is a very typical nameplate from a common Delta -> Wye step down transformer, you can see the 2 dashed lines on the primary and secondary showing a 30 degree phase shift between them. The dotted line on the Delta Primary is "angled" up 30 degrees and the dotted line of the Wye Secondary (at X0) is straight across with zero "angle"

View attachment 2579091

Your Delta to Delta coil setups are straightforward and as the current rises in any one primary coil, it does so at the same time in its secondary mate. So zero phase shift and the dotted lines in your nameplate at H1 and X1 show the same angle - with no shift between them.

This phase shift is mostly a nerdy thing and it is very common for them to get misinterpreted as some kind of grounding indications. But they are not, it's science yo ! ;)

Also, sorry this thread is sliding off the rails into the transformer weeds - I assume your motor problem is not related to your transformer.

Again - good luck!
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This is awesome…completely makes sense to me now. Thank you for taking the time to explain. Definitely didn’t derail because I’m understanding now what the overall scenario I have going on is. Just an update it seems as if the control coil to the contact is bad and not providing the necessary voltage to fully engage the contact, therefore closing our “low voltage” relay.
 
jim dungar said:
Not every transformer should be run backwards. As previously mentioned taps are an issue. Some small transformers, like machine tool units less than 3kVA may actually have compensating windings on their primary to account for losses in thier cheaper core construction. Finally there is the probability the increased inrush/energizing current may require primary side OCPD which exceeds the NEC limits.

[Soapbox]
The reality is the NEC has their restriction, for manufacturer approval, because too many installers do not follow manufacturers instructions, especially when they are not included with the equipment. This is similar to how SCCR requirements have been added to article 240, in addition to the historical ones in 110.9 and 110.10, or the specific prohibition of 2 grounded conductors I a termination that accepts 2 grounding conductors.[/soapbox]
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How many machines such as overhead cranes are both motors and generators depending on what they are doing? Although unusual I have put up 480 volt bridge cranes in buildings fed by 208 or 240 volt services and had to install a step up transformer.
 
Joethemechanic said:
How many machines such as overhead cranes are both motors and generators depending on what they are doing? Although unusual I have put up 480 volt bridge cranes in buildings fed by 208 or 240 volt services and had to install a step up transformer.
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This point comes up in discussion of transformers for PV systems. The fact is that all transformer action is bidirectional. Power can flow in either direction and the transformer will work just fine.

IMHO the distinction between primary and secondary has more to do with which side gets energized first or which side 'defines' the voltage of the whole setup.

In the case of regenerating induction motors or line interactive PV inverters and the like, the transformer gets energized from the utility side. The utility is defining the voltage of the whole system. But then the power flows _two_ the utility. IMHO in this situation the primary side is the utility side even though power is flowing to the utility.

-Jonathan
 
winnie said:
IMHO the distinction between primary and secondary has more to do with which side gets energized first or which side 'defines' the voltage of the whole setup.

-Jonathan
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Agree here with Jon, and I'll add a little extra...

Another way I think about the distinction between primary and secondary windings is which one(s) are wound closest to the steel core and which are wound on the outside. Lets call them the inner and the outer windings.

The outer windings are - typically – connected as the primary coils for 2 reasons. First, taps are normally on the primary windings and it’s physically easier to manufacture a transformer if the taps are on the outside coils. If the taps were on the inside windings it would be a nightmare to assemble.

Second, being farther away from the steel core, the outer windings are “slower” to magnetize the steel core when you energize the transformer. Slower is good from an inrush current pov. This is the reason why, when you backfeed a normal step down transformer, the inrush current can be problematic. It’s because you are energizing the inner windings, and being closer to the steel core, they can really magnetize the core quickly. If the residual magnetization left over in the core from the last shutdown is in the same orientation / direction as the first cycle of energizing current wants to push it, the core can get driven quite quickly into saturation for a cycle or 2. It's a random thing, but it's worse when you energize the inner coils as the primary.

Again, sorry for driving around in the transformer weeds ;)
 
jim dungar said:
Although they rarely, for most of the US, they evidently fo exist.
The high leg would be 415V.
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We have many 480 high leg open delta here, mostly feeding limited loads. A center pivot irrigation maybe. If it has electric well with more than maybe 20 HP they would prefer to go with full three phase wye transformer bank, though years ago they would go with delta and usually would been corner grounded. A few of them still around but have had the neutral conductor added and is now high leg delta.

Nominal high leg voltage is 216 volts to ground. Other two lines are 240 to ground. Unloaded the voltage is often near 500 which puts the unloaded voltage of high leg to ground closer to 433.
 
Joethemechanic said:
Yeah I was thinking about grid tie PV too. I've never seen the utility change the pole pig because of PV. Although they are under NESC
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Unless you your PV is a stand alone system with only intention of feeding power into grid. But most smaller applications they are supplying power for on site usage and excess is exported to grid. Pole pig probably has no need to change for majority of those. Would only be if the VA capacity of the PV is high enough a larger transformer is needed, even with the offset of customer usage factored in.
 
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